Hydrologic Impacts of Drainage Systems

Kristie J. FranzWilliam Simpkins, Özlem Acar, Alexander Morrison

Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA

Nandita Basu, Becca Scheler, Brandon Sloam, Larry WeberIIHR-Hydroscience and Engineering, University of Iowa, Iowa City, IA

Matt HelmersDepartment of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA

Rick CruseDepartment of Agronomy, Iowa State University, Ames, IA

Overview

• In 2011, the Iowa Economic Development Authority funded a study of hydrologic impacts of drainage systems

– Focus on changes in water quantity and timing in Iowa streams

• Joint effort between Iowa State University and the University of Iowa, Iowa Flood Center and Iowa Water Center

• Report submitted June 2014

Objectives

1) Synthesize current understanding of subsurface drainage on water partitioning

2) Quantify spatial and temporal heterogeneity of water fluxes in tile-drained landscapes

3) Identify factors affecting storage, residence times and pathways of water

4) Determine relationship between drainage and peak flow events

• Purpose to prevent

excess water from

inhibiting crop growth

during the growing

season

Tiling

• Artificial drainage of soil using subsurface tile drains and

surface drainage ditches has been occurring for over 100

years in the Midwest (Zucker and Brown, 1998)

Motivation• US flooding (2008, 2010) has

caused millions of dollars in property

and economic loss in agricultural

areas

• Large magnitude floods sparked renewed interest in the impacts of artificial drainage on streamflow hydrology

(June 18, 2008 - Source: David Greedy/Getty Images)

?

Lots of ideas/limited work• Tile drains receive water through 3 mechanisms: Surface

Intake, Groundwater flow, and Preferential flow

• Dries soil -> more storage during precipitation, more water moving through slower pathways (i.e. not surface runoff)

• Increases rate of flow through system -> contributes water to stream that would not be there otherwise, tile water moves faster than soil water

Surface Intake Groundwater flow Preferential flow

• Tile drains decrease peak flows in silty and clayey soils (Robinson, 1990)

• Increased peak flows in clayey soils due to desiccation cracks promoted by drying (Robinson 1999)

• Initial conditions have important impacts on response time, runoff and tile flow, making it hard to generalize results (Schwab et al., 1985; Robinson 1999; Vidon and Cuadra 2011)

• Models generally show decreased peak in clays and loams and increased peaks in sandier soils

Chapter 2: Literature

Motivation

• Despite some work, lack of quantitative descriptions of tiling impacts

• Mainly field scale studies rather than watershed scale

• More studies on water quality

– This study aimed to better understand drainage effects on water quantity

http://farmtilepro.weebly.com/benefits.html

Primary approaches

• Modeling

– Field Scale as an initial step

– Scaled up field scale model to watershed scale (DRAINMOD)

– Watershed scale hydrologic model (Mike-SHE)

– Fully coupled surface/ground water model with physically-based governing equations (HydroGeoSphere)

• Hydrograph separation to understand water partitioning

Modeling

• Manual calibration and validated using site data

• Synthetic studies also done using typical Iowa soils

Chapter 3: Field Scale Modeling

• Methodology• DRAINMOD - 1-D soil drainage model, water balance

• Soil Water Atmosphere Plant (SWAP) – unsaturated zone, Richard’s equation

– Models used to explore variations in soil type, structure, annual rainfall, and drainage spacing

Fig 3.7. USDA soil textural classes. Circles

indicate soils prevalent in Iowa .

Chapter 3: Field scaleSWAP and DRAINMOD simulations for different soil types

SWAP: Peak flow 1987-2012 Ames, IA precipitation

Figure 3.12, 3.22

DRAINMOD: Peak flow in clay soils 1981-2010 Iowa City precipitation

• Models do not reveal a significant difference • Slight decrease in peak flows under drained

conditions

• Slight increase in medium events under drainage

• Slight decrease in high events under drainage

DRAINMOD Runoff v. soil types

Fig: 3.25

High (75th percentile) rainfall

Medium (50th percentile) rainfall

DRAINMOD simulations for 7 major soil textural classes in Iowa1981-2010 state-wide data

Low (25th percentile) rainfall

Iowa Landform Regions

Chapter 4: Watershed Scale Modeling

DRAINMOD with geomorphic unit hydrograph to route from hillslope scale to watershed scale

Figure 4.6: Three drainage scenarios.Clear Creek Watershed (253 km2)

6359 hillslopes30 years of hourly rainfallEqually distributed across watershed

According to row crop land use

(2002)

Same percentage land drained

Watershed-scale DRAINMOD

• August 10-21, 1993

Figure 4.8

No significant difference in first event

All undrained highest peaks, followed by original (likely existing drainage conditions)

Watershed-scale DRAINMOD

• Comparison of tiling location

Figure 4.9

No significant difference in first event (larger event)

Near drained and all undrained produced highest peaks

Far drainage • water runs quickly off areas close to the

outlet and exits watershed early in event

Near drainage –• water near outlet is being routed through

slower subsurface pathways, so decreases the initial peak

• runoff from undrained land and tile flow combine to increase peak at the end of event

Watershed Scale MIKE-SHE

MIKE SHE - Physically based, watershed-scale model

Figure 4.15.

South Fork watershed TC242 basin of Tipton subbasin (1.6 km2)

Simulated 2005-2012

Tile outflow observations to calibrate drainage time constant

3 scenarios• partial drainage in lowland soils

only (common practice)• All drained• No drainage

Watershed scale - MIKE SHE2008 simulation – largest precipitation events in time period

Figure 4.22: “Actual flow” is the observed flow from the tile outlet of TC242.

higher peaks under drainage in smaller event

lower peaks under drainage in two larger events

Figure 4.21: “Actual flow” is the observed flow from the tile outlet of TC242.

2007 simulation – normal year

Higher peaks with drainage

Watershed scale - MIKE SHE

Lower peaks with no drainage

Chapter 5 Water partitioning• Stable isotopes used as a signature of where the water has

been and how it got to the stream– South Fork watershed

– Samples collected from groundwater, surface water, tile water and precipitation from August 2011 – July 2013

Chapter 5 Water partitioning

Overlap early in period

Drought: tile water and groundwater overlap -> tile water sourced from groundwater

Rain: tile water and surface water overlap, tile water separates from groundwater signal

Drainage Contribution using Stable Isotopes• Observations were limited but support the following model

– Drought and normal conditions: tile water mainly groundwater

– Heavy rainfall: tile water dominated by precipitation

Chapter 6: Major Findings

• Field and watershed scale model results

– Support reduction of peak flows for intense events (or no impact) under tile drainage compared to no drainage

– Placement of drains and timing of precipitation modifies this reduction

– Degree of tile impact varied by models • Scale of analysis or model structure likely influencing results

(MIKE-SHE tended to have more dramatic impact, but was applied at smallest watershed scale)

• Careful consideration of modeling approach should be taken

Chapter 6: Major Findings

• Modeling and Isotope analyses show

– Low to moderate flows are increased

– Overall water output is increased

– During dry conditions drains are tapping into water sources that would otherwise not be contributing to streamflow

Challenges• Difficulty in validating models because observations of

all hydrologic components are lacking

– TC242 had no surface runoff observations

– Clear Creek had no tile observations

– One nearby precipitation gage in many cases

– Where are the tiles?

• As models become more realistic (complex and physically-based), they become more difficult to run at large scales

– Most models provided limited treatment of transpiration (e.g. water logging of plants)

Acknowledgements

• Funding for this work was provided by the Iowa Economic Development Authority.

http://ir.uiowa.edu/cgi/viewcontent.cgi?article=4759&context=etd

IIHR Technical Report No. 486 available at:

Questions ?

Future Work

• Explore HGS for hydrologic modeling of tiled watersheds; effectively eliminates the uncertainty regarding conceptualization, scale applicability, and parameterization of tile behavior in models

• Look into the impact of surface inlets

Background• River discharge has traditionally been assumed

stationary, though this is no longer thought to be the case (Milly et al., 2008)

• Increasing precipitation alone insufficient to explain

increasing trends in discharge in Midwest agricultural

watersheds (Schilling and Libra, 2003; Raymond et al., 2008)

• Land use change and management more important than

climatic changes for observed increases in Mississippi

River discharge (Raymond et al., 2008)

• Climate change thought to be the larger factor in

streamflow increases in the Midwest (Tomer and Schilling, 2009)

• Steffens and Franz (2012) concluded that mean daily

discharge (in Iowa watersheds) may be increasing

regardless of changing watershed characteristics

Most comprehensive discussion

• Robinson (1990) Most studies suggest subsurface drains decrease peak flows in clayey soils and increase peak flows in sandy soils

DRAINMOD

• Deterministic, hydrologic model used to simulate soil-regime on drainage landscapes

– Predicts surface runoff, infiltration, ET, subsurface drainage, and seepage

– Calibrated with data from 1990-1993, validated from 1994-2003

HydroGeoSphere

• Addition of tile drainage system resulted in large water balance errors– Created numerical

instability in the solution

• Need to define tile boundary condition to eliminate unrealistic tile flow results

Evaluation of models

• DRAINMOD• Despite simplifications, combined DRAINMOD and

routing models applied at watershed scale capture hydrograph responses at the outlet

• MIKE SHE• Performed satisfactory for reproducing watershed

discharge for TC242 and exploring the impact of tiling on watershed response

• HydroGeoSphere• Holds promise in determining the impacts on tile

drainage system on the hydrology

• Improvements in near future will allow it to realize its full potential